I. Field
The present invention relates to systems and methods for interference cancellation, and, more specifically, the use of optical techniques in systems and methods for interference cancellation.
II. Background
Radio-frequency (RF) and microwave signals are commonly employed in wireless communications due to their desirable propagation characteristics. To minimize losses and distortion, systems often transmit the signals at higher power levels to minimize the losses and distortion that may result. At the receiving end, the signals are inevitably received at power levels significantly lower than the power levels used for transmission. If a transmitter and receiver are co-located, this can cause significant difficulties because the transmitted signal can interfere with the desired received signal and in some cases may overpower the received signal such that it is buried under the locally transmitted signal. In addition to interference generated by transmitters that are co-located with the receiver, other sources of interference at the receiver can include multi-path “echoes” originating from the co-located transmit signal where such multipath interference can be created from both static object (e.g., a building) and dynamic objects (e.g., a moving car), and can also include a remote interferer (such as a jammer). Moreover, in the case of the remote interference, no prior knowledge of the interference is assumed.
A variety of electronic methods for interference cancellation have been developed and currently are in use. For example, U.S. Pat. No. 6,724,840 entitled “Adaptive Interference Cancellation Method” discusses ‘the design and performance of an analog cancellation system. The system generates either narrow or wideband nulls in order to minimize the effect of interfering signals on a receiver. A microcontroller directs the detection and classification of the interfering signal relative to frequency, amplitude and modulation, such as pulse-width or continuous wave modulation. A sampled version of the interfering signal at frequency, fi, is phase-inverted, amplified, and vector-summed with the input signal stream to null the interfering signal at fi. The microcontroller also monitors and adjusts the cancellation system's circuit parameters to minimize any residual interfering signal at fi or respond to changes in the interference. In another example, U.S. Pat. No. 7,366,244 discloses a cancellation device that attempts to suppress antenna interference by generating an estimate of the interference signal and subtracting the estimate from the interference signal. The cancellation device can generate the estimate based on sampling signals on an antenna that generates the interference or on an antenna that receives the interference. The cancellation device can comprise a model of the crosstalk effect. Transmitting test signals on the communication system can define or refine the model.